Sydney Y. Schaefer

Hemispheric Specialization and Functional Impact of Ipsilesional Deficits in Movement Coordination and Accuracy

Previous studies have demonstrated that following unilateral stroke, motor impairment occurs both contralateral, as well as ipsilateral, to the lesion. Although ipsilesional impairments can be functionally limiting, they can also provide important insight into the role of the ipsilateral hemisphere in controlling movement and the lateralization of specific motor control mechanisms, given that unilateral arm movements are thought to recruit processes in each hemisphere. The purpose of this study was to examine whether left and right hemisphere damage following stroke produces different ipsilesional deficits, and whether our dynamic dominance model of motor lateralization can predict such deficits. Specifically, the dynamic dominance model attributes control of multijoint dynamics to the left hemisphere, and control of steady-state position to the right hemisphere. Chronic stroke patients with either left or right hemisphere damage (LHD or RHD) used their ipsilesional arm, and the control subjects used either their left or right arm (LHC or RHC), to perform targeted reaching movements in different directions within the workspace ipsilateral to their reaching arm. We found that the LHD group showed deficits in controlling the arms trajectory due to impaired multijoint coordination, but no deficits in achieving accurate final positions. In contrast, the RHD group showed deficits in final position accuracy but not in the ability to coordinate multiple joints during movement, thereby providing additional evidence for the hemisphere-specific nature of motor deficits. Furthermore, while both the LHD and RHD groups were functionally impaired to the same degree on the Jebsen Hand Function Test (JHFT), our results suggest that the underlying mechanisms for such impairment may be hemisphere-dependent.

Assessment of upper extremity impairment, function, and activity after stroke: Foundations for clinical decision making

The purpose of this review is to provide a comprehensive approach for assessing the upper extremity (UE) after stroke. First, common UE impairments and how to assess them are briefly discussed. Although multiple UE impairments are typically present after stroke, the severity of ones impairment, paresis, is the primary determinant of UE functional loss. Second, UE function is operationally defined and a number of clinical measures are discussed. It is important to consider how impairment and loss of function affect UE activity outside of the clinical environment. Thus, this review also identifies accelerometry as an objective method for assessing UE activity in daily life. Finally, the role that each of these levels of assessment should play in clinical decision making is discussed to optimize the provision of stroke rehabilitation services.

Dissociation of initial trajectory and final position errors during visuomotor adaptation following unilateral stroke

Previous studies have demonstrated that following stroke, motor impairment can occur ipsilateral to the lesion. Such impairments have provided insight into the contributions of each hemisphere to movement control, showing that left and right hemisphere damage produce different effects on movement: Left hemisphere damage produces deficits in specifying features of movement trajectory, while right hemisphere damage produces deficits in achieving an accurate and stable final position. We now propose that left and right hemisphere damage should also produce different deficits in the adaptation of trajectory and position. To test this idea, we examined adaptation to visuomotor rotations in the ipsilesional arms of hemiparetic stroke patients with left (LHD) and right hemisphere damage (RHD). We found that LHD interfered with adaptation of initial direction, but not with the ability to adapt the final position of the limb. In contrast, RHD interfered with online corrections to the final position during the course of adaptation. These findings support our hypothesis that the control of trajectory and steady-state position may be lateralized to the left and right hemispheres, respectively.

Transfer of Training Between Distinct Motor Tasks After Stroke: Implications for Task- Specific Approaches to Upper-Extremity Neurorehabilitation

Background. Although task-specific training is emerging as a viable approach for recovering motor function after stroke, there is little evidence for whether the effects of such training transfer to other functional motor tasks not directly practiced in therapy. Objective. The purpose of the current study was to test whether training on one motor task in individuals with chronic hemiparesis poststroke would transfer to untrained tasks that were either spatiotemporally similar or different. Methods. In all, 11 participants with chronic mild to moderate hemiparesis following stroke completed 5 days of supervised massed practice of a feeding task with their affected side. Performance on the feeding task, along with 2 other untrained functional upper-extremity motor tasks (sorting, dressing) was assessed before and after training. Results. Performance of all 3 tasks improved significantly after training exclusively on 1 motor task. The amount of improvement in the untrained tasks was comparable and was not dependent on the degree of similarity to the trained task. Conclusions. Because the number and type of tasks that can be practiced are often limited within standard stroke rehabilitation, results from this study will be useful for designing task-specific training plans to maximize therapy benefits.

Need for speed: better movement quality during faster task performance after stroke.

Background. Although slow and insufficient muscle activation is a hallmark of hemiparesis poststroke, movement speed is rarely emphasized during upper-extremity rehabilitation. Moving faster may increase the intensity of task-specific training, but positive and/or negative effects on paretic-limb movement quality are unknown. Objective. To determine whether moving quickly instead of at a preferred speed either enhances or impairs paretic-limb task performance after stroke. Methods. A total of 16 people with poststroke hemiparesis and 11 healthy controls performed reach–grasp–lift movements at their preferred speed and as fast as possible, using palmar and 3-finger grip types. The authors measured durations of the reach and grasp phases, straightness of the reach path, thumb–index finger separation (aperture), efficiency of finger movement, and grip force. Results. Reach and grasp phase durations decreased in the fast condition in both groups, showing that participants were able to move more quickly when asked. When moving fast, the hemiparetic group had reach durations equal to those of healthy controls moving at their preferred speed. Movement quality also improved. Reach paths were straighter, and peak apertures were greater in both groups in the fast condition. The group with hemiparesis also showed improved efficiency of finger movement. Differences in peak grip force across speed conditions did not reach significance. Conclusions. People with hemiparesis who can perform reach–grasp–lift movements with a 3-finger grip can move faster than they choose to, and when they do, movement quality improves. Simple instructions to move faster could be a cost-free and effective means of increasing rehabilitation intensity after stroke.

Ipsilesional trajectory control is related to contralesional arm paralysis after left hemisphere damage

We have recently shown ipsilateral dynamic deficits in trajectory control are present in left hemisphere damaged (LHD) patients with paresis, as evidenced by impaired modulation of torque amplitude as response amplitude increases. The purpose of the current study is to determine if these ipsilateral deficits are more common with contralateral hemiparesis and greater damage to the motor system, as evidenced by structural imaging. Three groups of right-handed subjects (healthy controls, LHD stroke patients with and without upper extremity paresis) performed single-joint elbow movements of varying amplitudes with their left arm in the left hemispace. Only the paretic group demonstrated dynamic deficits characterized by decreased modulation of peak torque (reflected by peak acceleration changes) as response amplitude increased. These results could not be attributed to lesion volume or peak velocity as neither variable differed across the groups. However, the paretic group had damage to a larger number of areas within the motor system than the non-paretic group suggesting that such damage increases the probability of ipsilesional deficits in dynamic control for modulating torque amplitude after left hemisphere damage.

Beside the point: motor adaptation without feedback-based error correction in task-irrelevant conditions.

Adaptation of movement may be driven by the difference between planned and actual motor performance, or the difference between expected and actual sensory consequences of movement. To identify how the nervous system differentially uses these signals, we asked: does motor adaptation occur when movement errors are irrelevant to the task goal? Participants reached on a digitizing tablet from a fixed start location to one of three targets: a point, an arc, or a ray. For the arc, reaches could be in any direction, but to a specific extent. For the ray, reaches could be to any distance, but in a targeted direction. After baseline reaching to the point, the direction or extent of continuous visual feedback was perturbed during training with either a cursor rotation or gain, respectively, while reaching to either the ray (goal = direction) or the arc (goal = extent). The perturbation, therefore, was either relevant or irrelevant to the task goal, depending on target type. During interspersed catch trials, the perturbation was removed and the target switched back to the point, identical to baseline. Although the goal of baseline and catch trials was the same, significant aftereffects in catch trials indicated behavioral adaptation in response to the perturbation. Adaptation occurred regardless of whether the perturbation was relevant to the task, and it was independent of feedback control. The presence of adaptation orthogonal to task demands supports the hypothesis that the nervous system can rely on sensory prediction to drive motor learning that can generalize across tasks.

Using Dual Tasks to Test Immediate Transfer of Training Between Naturalistic Movements: A Proof-of-Principle Study

ABSTRACT Theories of motor learning predict that training a movement reduces the amount of attention needed for its performance (i.e., more automatic). If training one movement transfers, then the amount of attention needed for performing a second movement should also be reduced, as measured under dual task conditions. The authors’ purpose was to test whether dual task paradigms are feasible for detecting transfer of training between two naturalistic movements. Immediately following motor training, subjects improved performance of a second untrained movement under single and dual task conditions. Subjects with no training did not. Improved performance in the untrained movement was likely due to transfer, and suggests that dual tasks may be feasible for detecting transfer between naturalistic actions.

Short-term practice effects in mild cognitive impairment: Evaluating different methods of change

ABSTRACT Practice effects are improvements on cognitive tests as a result of repeated exposure to testing material. However, variability exists in the literature about whether patients with amnestic mild cognitive impairment (MCI) display practice effects, which may be partially due to the methods used to calculate these changes on repeated tests. The purpose of the current study was to examine multiple methods of assessing short-term practice effects in 58 older adults with MCI. The cognitive battery, which included tests of memory (Hopkins Verbal Learning Test–Revised and Brief Visuospatial Memory Test–Revised) and processing speed (Symbol Digit Modalities Test and Trail Making Test Parts A and B), was administered twice across one week. Dependent t tests showed statistically significant improvement on memory scores (ps < .01, ds = 0.8–1.3), but not on processing speed scores. Despite this, the sample showed no clinically meaningful improvement on any cognitive scores using three different reliable change indices. Regression-based change scores did identify relatively large groups of participants who showed smaller than expected practice effects, which may indicate that this method is more sensitive in identifying individuals who may portend a declining trajectory. Practice effects remain a complex construct, worthy of continued investigation in diverse clinical conditions.

Asking New Questions with Old Data: The Centralized Open-Access Rehabilitation Database for Stroke.

Background This paper introduces a tool for streamlining data integration in rehabilitation science, the Centralized Open-Access Rehabilitation database for Stroke (SCOAR), which allows researchers to quickly visualize relationships among variables, efficiently share data, generate hypotheses, and enhance clinical trial design. Methods Bibliographic databases were searched according to inclusion criteria leaving 2,892 titles that were further screened to 514 manuscripts to be screened by full text, leaving 215 randomized controlled trials (RCTs) in the database (489 independent groups representing 12,847 patients). Demographic, methodological, and statistical data were extracted by independent coders and entered into SCOAR. Results Trial data came from 114 locations in 27 different countries and represented patients with a wide range of ages, 62 year [41; 85] [shown as median (range)] and at various stages of recovery following their stroke, 141 days [1; 3372]. There was considerable variation in the dose of therapy that patients received, 20 h [0; 221], over interventions of different durations, 28 days [10; 365]. There was also a lack of common data elements (CDEs) across trials, but this lack of CDEs was most pronounced for baseline assessments of patient impairment and severity of stroke. Conclusion Data integration across hundreds of RCTs allows clinicians and researchers to quickly visualize data from the history of the field and lays the foundation for making SCOAR a living database to which researchers can upload new data as trial results are published. SCOAR is a useful tool for clinicians and researchers that will facilitate data visualization, data sharing, the finding of relevant past studies, and the design of clinical trials by enabling more accurate and comprehensive power analyses. Furthermore, these data speak to the need for CDEs specific to stroke rehabilitation in randomized controlled trials. PROSPERO 2014 CRD42014009010